HDR brachytherapy is a form of cancer therapy that utilizes high doses of ionizing radiation delivered over a short period of time, i.e., for instance, in some minutes, directly at or near the target. Since the delivered doses are relatively high, only a very small margin of error regarding dwell positions, where the doses are applied, and dwell times defining the time periods of applying the doses at the dwell positions is acceptable. It is therefore essential to be able to develop an accurate treatment plan, which defines the dwell positions and the dwell times, and to accurately deliver radiation according to this treatment plan. The treatment plan is generally developed based on a segmented ultrasound image in which the target and the brachytherapy catheters used for delivering the doses are segmented. For developing a very accurate treatment plan it is therefore required to very accurately segment the target and the brachytherapy catheters in the ultrasound image. However, the inherent ultrasonic contrast between a) the target and the brachytherapy catheters and b) their surrounding is often relatively low, which may lead to a not very accurate segmentation of the target and the brachytherapy catheters in the ultrasound image and, thus, to a not very accurate HDR brachytherapy.